The present invention relates to a semiconductor processing article and to a system to process semiconductors in a low pressure chemical vapor deposition furnace.
Low pressure chemical vapor deposition (LPCVD) is a film forming process for the production of semiconductor devices. The process is used in the formation of layers such as silicon nitride, silicon dioxide and polysilicon on a silicon wafer substrate. Low pressure techniques, for example in the range of 0.5-3 torr have advantages in terms of uniformity in processing. Typically in the process, a substrate is placed in a reaction chamber, which is heated and brought to a low pressure state. A reaction gas is introduced into the chamber, and reaction material is deposited on the substrate either by reaction or by thermal decomposition of the reaction gas.
The deposition is typically conducted at temperatures between 550xc2x0 C. and 950xc2x0 C., at a pressure of about 1 torr using processing articles that include, for example, a liner, process tube, shield, baffle, paddle, cantilever arm, carrier or boat made out of fused quartz. Since the processing articles are at the same temperature as the wafer substrate, the articles are coated at every run with a layer as thick as the layer deposited on the substrate. After many runs, each article is covered with a thick film build-up. The film build-up causes a stress from the coefficient of thermal expansion (CTE) difference between silicon (2.9 ppm/xc2x0 C.) or silicon nitride (5.0 ppm/xc2x0 C.) and quartz (0.5 ppm/xc2x0 C.). Eventually, this stress induces cracking in the surface of the quartz. Articles such as wafer carriers or boats and related cantilever arms are more prone to crack formation because they are cycled from the process chamber temperature to room temperature with each run to allow loading and unloading of wafers. Additionally, film buildup results in flakes that contaminate the semiconductor products and cause defects in the layers being formed. Unless the film deposited on each article is frequently removed, it will contaminate the substrate during processing, significantly degrading device yield.
The processing articles can be cleaned to remove film build-up. Typically, the articles are cleaned after a build-up of a film 5-10 microns thick. Cleaning the articles is time consuming and requires shut down of the LPCVD processing equipment. Also, frequent cleaning can lengthen micro cracks in the quartz. Micro cracks promote brittleness and contribute to part failure. There is a need to eliminate the adverse effects of film build-up on LPCVD furnace processing articles without increased cleaning.
The invention relates to a semiconductor processing article that is characterized by extended useful life. The article can be used in a semiconductor furnace system, particularly in a LPCVD furnace for prolonged periods without requiring cleaning to remove build-up film. The semiconductor processing article typically comprises a quartz body characterized by a surface roughness having a first component with an average deviation from a first mean surface of about 2.5 to 50 microns, and a second component with an average deviation from a second mean surface of about 0.25 to 5 microns. The processing article is prepared for use in the furnace by mechanically roughening and chemically roughening the quartz surface of the article.
In another aspect, the invention relates to a heat treatment process, comprising preparing a quartz processing article by mechanically blasting and chemically etching the surface of the article. The article is then installed into a processing chamber of a chemical vapor deposition furnace. A substrate to be treated is loaded into the processing chamber and a treatment gas is supplied into the processing chamber to form a film on the substrate.